Thin-film magnetic head, magnetoresistance effect magnetic head and composite magnetic head

ABSTRACT

A thin-film magnetic head, a magnetoresistance effect magnetic head and an MR inductive head are disclosed. The thin-film magnetic head has one of thin-film magnetic cores stacked on a substrate and formed of two magnetic films and a non-magnetic film held between them, with a current flowing through the thin-film magnetic core in the direction of hard axis thereof. The magnetoresistance effect magnetic head has one of a pair of shield cores having a magnetoresistive element between them formed of two magnetic films and a non-magnetic film held between them, the magnetoresistive element being electrically connected to the shield core, with a sense current flowing through the shield core. The current flowing through the one shield core via the magnetoresistive element is preferably an AC of decrement amplitude for demagnetizing the shield core along with a DC sense current. Also, this current preferably flows in the direction of hard axis of the shield core so that magnetic properties of the shield core are stabilized or demagnetized by the magnetic field generated in the direction of easy axis. The MR inductive head has a second thin-film magnetic core as a common magnetic body of an MR head and an inductive head on one substrate, formed of two magnetic films and a non-magnetic film held between them, with a current flowing through the second thin-film magnetic core in the direction of hard axis thereof.

This is a continuation of application Ser. No. 08/598,739, filed Feb. 8,1996, now abandoned, which in turn is a continuation of application Ser.No. 08/274,323 filed Jul. 13, 1994, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a thin-film magnetic head, a magnetoresistanceeffect magnetic head and a composite magnetic head which are suitablyadapted for recording and reproducing information signals into and from,for example, a hard disk.

A magnetoresistance effect magnetic head, hereinafter referred to as anMR head, has its magnetic sensor formed of a magnetic thin film havingmagnetoresistance effect. Since resistivity of the magnetic thin film ischanged in accordance with a signal magnetic field based on magneticrecording into a magnetic recording medium, the magnetic sensor detectsthe change in resistivity as a reproduction output voltage from a sensecurrent flowing through the magnetic thin film.

Such an MR head has characteristics, such as, high output, low crosstalkand velocity-independence, and is therefore used as a reproducing headfor a hard disk drive (HDD) or as a high density recording/reproducinghead for a digital audio tape recorder.

This MR head is exemplified by an MR head of shield structure as shownin FIG. 1.

The shield MR head 100 of FIG. 1 has an MR element 101, which is formedof a single-layer or multi-layer magnetic thin film havingmagnetoresistance effect and is arranged in a space forming apredetermined reproduction gap G_(R) between an upper (layer) shieldcore 102 and a lower (layer) shield core 103. The MR element 101 iselectrically connected with a pair of electrodes 105a, 105b for causinga direct current as the sense current to flow and for outputting thechange in resistivity as a change in voltage.

Between the electrodes 105a, 105b, a bias conductor 104 for applying abias magnetic field to the MR element 101 is provided, traversing the MRelement 101. For the shield cores 102, 103 of the shield MR head 100, asingle bulk magnetic body, a single-layer plating film or a single-layersputtered film is used.

An example of a composite magnetic head, produced by combining an MRhead with a recording head formed of an inductive thin-film magnetichead, is shown in FIG. 2. The inductive thin-film magnetic head and thecomposite magnetic head are hereinafter referred to as an inductive headand an MR inductive head, respectively. Since the MR head in this casehas the structure similar to that of the example in FIG. 1, thecorresponding parts are denoted by the same reference numerals and willnot be explained further.

In FIG. 2, a magnetic core 106 is provided on the upper shield core 102of the MR head with a predetermined recording gap G_(w) between them,and a spiral head winding 107 is provided, surrounding a magneticallyconnecting part as a connecting portion of the magnetic core 106 withthe shield core 102.

In the MR inductive head of this structure, the lower shield core 103 isprovided on a base or substrate 108 of Al₂ O₃ -TiC, and a protectionfilm layer 109 is stacked on the magnetic core 106, with a non-magneticinsulation material charged or stacked between the gaps. The end surfaceof the MR inductive head having the reproduction gap G_(R) and therecording gap G_(w) formed therein serves as an air bearing surface(ABS), that is, a surface facing the magnetic recording medium, such asa hard disk.

Meanwhile, the magnetic core 106 and the shield cores 102, 103 arenormally provided with anisotropy in a particular direction, that is,the direction of track width, in the production process. However, it isdifficult to provide anisotropy on the entire film of the magnetic core106 and the shield cores 102, 103, and dispersion of anisotropy usuallyremains in a microscopic sense. Such dispersion of anisotropy is a causeof a noise generated by fluctuation in output and shifting of magneticdomain walls, that is, a so-called Barkhausen noise. Also, the magneticununiformity causes fluctuation at the time when the magnetic field isexternally added, resulting in fluctuation of reproduction output afterrecording.

If a two-gap recording/reproducing head is employed in which theinductive head is superposed on the MR head, or if a one-gaprecording/reproducing head is employed in which the magnetic core of theinductive head serves also as the shield core of the MR head, a largemagnetic field is applied from a recording head section to the shieldcore on recording. For this reason, a magnetic domain of the shield coremay remain turbulent when the operation has been switched from recordingto reproduction. Since the shield core forms part of a magnetic path ofthe magnetic field from the magnetic medium, there is a high possibilitythat the turbulence of the magnetic domain of the shield core causes theBarkhausen noise to be generated. In addition, since the shield coreforms part of a magnetic path of the magnetic bias, the state of biasbecomes unstable, causing the reproduction signal waveform to beunstable.

The JP Patent Kokai Publication No. 5-62131, for example, discloses atechnique of maintaining a reproduction output at a constant level bysplitting the thin-film magnetic core into two films with thenon-magnetic layer between them and then reducing the leakage magneticfield from the thin-film magnetic core to the MR element. Also, attemptsto restrict changes in the magnetic domain due to the recording magneticfield have been made with the use of a shield core formed of a magneticfilm of two layers or more which is separated with the non-magnetic filmand stacked. However, it is difficult to perfectly stabilize themagnetic domain and to have a perfectly single magnetic domain forstabilizing reproduction signals.

Meanwhile, it has been known that the Barkhausen noise can be reduced byapplying the magnetic field in the direction of the easy axis. Thus, atechnique of causing a current to flow through the two-layer shield coreto stabilize the reproduction output has been conceived. However, evenwith this technique, it may be impossible to perfectly adjust themagnetic domain which has become turbulent on recording, particularly inthe MR inductive head.

SUMMARY OF THE INVENTION

In view of the above-described status of the art, it is an object of thepresent invention to provide a thin-film magnetic head, amagnetoresistance effect magnetic head and an MR inductive head, whichhave magnetic domains of thin-film magnetic core and the shield corestabilized or demagnetized and have head outputs improved while havingrelatively simple structure.

According to the present invention, there is provided a thin-filmmagnetic head having one of thin-film magnetic cores stacked on asubstrate and formed of two magnetic films and a non-magnetic film heldbetween them, with a current being caused to flow through the thin-filmmagnetic core in the direction of hard axis thereof.

According to the present invention, there is also provided amagnetoresistance effect magnetic head having one of a pair of shieldcores having a magnetoresistive element between them formed of twomagnetic films and a non-magnetic film held between them, themagnetoresistive element being electrically connected to the shieldcore, with a sense current being caused to flow through the shield core.

In this case, the current flowing through the one shield core via themagnetoresistive element may be preferably an AC of decrement amplitudefor demagnetizing the shield core along with a DC sense current. It isalso preferred that this current flows in the direction of hard axis ofthe shield core so that magnetic properties of the shield core arestabilized or demagnetized by the magnetic field generated in thedirection of easy axis.

According to the present invention, there is also provided an MRinductive head having a second thin-film magnetic core used as a commonmagnetic body of an MR head and an inductive head on one substrate andformed of two magnetic films and a non-magnetic film held between them,with a current being caused to flow through the second thin-filmmagnetic core in the direction of hard axis thereof.

In the thin-film magnetic head according to the present invention, asthe current flows through the thin-film magnetic core in the directionof hard axis thereof, the current generates a magnetic field in thedirection of easy axis, and this magnetic field adjusts the magneticdomain of the thin-film magnetic core into the direction of easy axis,thus stabilizing the magnetic domain.

In the MR head according to the present invention, as the shield core iselectrically connected to the MR element so that the sense current flowsthrough the shield core via the MR element, the current generates amagnetic field in the direction of easy axis, and this magnetic fieldadjusts the magnetic domain of the thin-film magnetic core into thedirection of easy axis, thus stabilizing the magnetic domain.

In the MR inductive head according to the present invention, as thecurrent flows through the second thin-film magnetic core as the commonmagnetic body of the MR head and the inductive head in the direction ofhard axis of the thin-film magnetic core, the current generates amagnetic field in the direction of easy axis, and this magnetic fieldadjusts the magnetic domain of the thin-film magnetic core into thedirection of easy axis, thus stabilizing the magnetic domain.Accordingly, the magnetic domain which has become turbulent afterrecording with the inductive head can be stabilized by the magneticfield generated by the current flowing through the second thin-filmmagnetic core. As a result, fluctuation in output and generation of theBarkhausen noise can be significantly reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view showing the structure of aconventional shield MR head.

FIG. 2 is a schematic cross-sectional view showing the structure of aconventional MR inductive head.

FIG. 3 is an enlarged cross-sectional view showing essential portions ofa thin-film magnetic head of Embodiment 1.

FIG. 4 is an enlarged plan view showing an upper layer thin-filmmagnetic core of the thin-film magnetic head of Embodiment 1.

FIG. 5 is a schematic view showing a state of magnetic field generationat the time when a current in the direction of hard axis is caused toflow through the upper layer thin-film magnetic core of the thin-filmmagnetic head of Embodiment 1.

FIG. 6 is a schematic perspective view showing the structure of an MRhead of Embodiment 2.

FIG. 7 is an enlarged cross-sectional view showing the MR head ofEmbodiment 2.

FIG. 8 is a schematic view showing a state of magnetic field generationat the time when a current in the direction of hard axis is caused toflow through a shield core of the MR head of Embodiment 2.

FIG. 9 is an enlarged cross-sectional view showing essential portions ofan MR inductive head of Embodiment 3.

FIG. 10 is an enlarged front view showing the MR inductive head ofEmbodiment 3, as viewed from the ABS surface.

FIG. 11 is a block circuit diagram showing an example of a circuitstructure employed in the MR inductive head of Embodiment 3.

FIGS. 12A through 12D are waveform diagrams for explaining an example ofa current supplies to an MR head of the MR inductive head of Embodiment3. FIG. 12A shows changes in the reproduction/recording (R/W) mode. FIG.12B shows a sense current (DC) in the recording mode. FIG. 12C shows adecrement demagnetization current (AC). FIG. 12D shows a state in whichthe demagnetization current has been superposed on the sense current.

FIG. 13 is block circuit diagram showing a concrete example of ademagnetization current control voltage generation circuit and a sensecurrent control voltage generation circuit of the MR inductive head ofEmbodiment 3.

FIG. 14 is a waveform diagram showing another example of the currentsupplied to the MR head of the MR inductive head of Embodiment 3.

FIG. 15 is a block circuit diagram showing another example of thecircuit structure employed in the MR inductive head of Embodiment 3.

FIG. 16 is a block circuit diagram showing still another example of thecircuit structure employed in the MR inductive head of Embodiment 3.

FIG. 17 is an enlarged cross-sectional view showing essential portionsof an MR inductive head of Embodiment 4.

FIG. 18 is an enlarged front view showing essential portions of the MRinductive head of Embodiment 4, as viewed from the ABS surface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

Embodiment 1

In Embodiment 1, the present invention is applied to a thin-filmmagnetic head for recording/reproduction.

The thin-film magnetic head includes a pair of thin-film magnetic cores2, 3 stacked on a substrate 1 of, for example, Al₂ O₃ -TiC, and amagnetic gap G_(RW) serving as a recording/ reproduction gap formedbetween forward ends of the thin-film magnetic cores 2, 3, as shown inFIG. 3.

A magnetic circuit section is constituted by the lower thin-filmmagnetic core 2 formed on the substrate 1, the upper thin-film magneticcore 3 formed on the lower thin-film magnetic core 2 with apredetermined distance therefrom, and a conductive coil 4 formed betweenthese thin-film magnetic cores 2, 3.

The lower thin-film magnetic core 2 is formed across the portion fromthe side of an ABS surface 5 in which the magnetic gap G_(RW) ispresented to the back side, with one lateral edge exposed to the ABSsurface 5.

The upper thin-film magnetic core 3 is also formed across the portionfrom the side of the ABS surface 5 to the back side, with one lateraledge exposed to the ABS surface 5. The upper thin-film magnetic core 3is provided closely to the lower thin-film magnetic core 2 on the ABSsurface, thus forming the magnetic gap G_(RW) in the portion where thethin-film magnetic cores 3, 2 are close to each other. Also, the upperthin-film magnetic core 3 is inclined backward from the zero-depthposition of the magnetic gap G_(RW) in such a manner as to have anincreasing distance from the lower thin-film magnetic core 2, and iscaused to be in parallel to the lower thin-film magnetic core 2 from theintermediate portion. The upper thin-film magnetic core 3 is then causedto magnetically contact the lower thin-film magnetic core 2 on the backside.

The upper thin-film magnetic core 3 has a stacked structure constitutedby two layers of magnetic films 6, 7 and a non-magnetic film 8 heldbetween them.

The conductive coil 4 is formed in a spiral shape by sputtering aconductive metallic material, such as Cu or Al, and then etching thesputtered material. The conductive coil 4 is buried in an insulationlayer 9 formed between the lower thin-film magnetic core 2 and the upperthin-film magnetic core 3, and is formed around the magneticallyconnecting portion of the lower and upper thin-film magnetic cores 2, 3.

For protecting the magnetic circuit section of the above structure, aprotection film 10 of, for example, Al₂ O₃ is formed on the upperthin-film magnetic core 3.

A ferromagnetic material having high saturation magnetic flux densityand satisfactory soft magnetic property is used for the lower thin-filmmagnetic core 2 and the upper thin-film magnetic core 3. Any ofconventionally known ferromagnetic materials can be used regardless ofits being crystalline or amorphous.

For example, ferromagnetic materials, such as, Fe-Al-Si based alloy,Fe-Al based alloy, Fe-Si-Co based alloy, Fe-Ni based alloy, Fe-Si-Cobased alloy, Fe-Al-Ge based alloy, Fe-Ga-Ge based alloy, Fe-Si-Ge basedalloy and Fe-Co-Si-Al based alloy, or Fe-Ga-Si based alloy may be used.In addition, in order to further improve corrosion resistance andabrasion resistance of the Fe-Ga-Si based alloy, an alloy having afundamental composition consisting of Fe, Ga, Co (including Co partlyreplacing Fe) to which at least one of Ti, Cr, Mn, Zr, Nb, Mo, Ta, W,Ru, Os, Rh, Ir, Re, Ni, Pb, Pt, Hf and V is added may be used.

Also, a ferromagnetic amorphous metal alloy or a so-called amorphousalloy may be used, such as, an alloy composed of at least one or moreelements of Fe, Ni and Co and at least one or more elements of P, C, Band Si, a metal-metalloid based amorphous alloy composed mainly of theabove-mentioned alloy and containing Al, Ge, Be, Sn, In, Mo, W, Ti, Mn,Cr, Zr, Hf and Nb, and a metal-metal based amorphous alloy composedmainly of a transition metal element of Co, Hf or Zr, or a rare earthelement.

As the film forming method for the thin-film magnetic cores 2, 3, theplating method or the vacuum thin film forming technique represented bythe vacuum deposition method, the sputtering method, the ion platingmethod or the cluster ion beam method is employed.

Meanwhile, the lower thin-film magnetic core 2 and the upper thin-filmmagnetic core 3 are provided with anisotropy in the production processso that the easy axis is in the direction of track width, indicated byarrow Y in FIG. 4, in parallel to a magnetic recording medium 11. Theanisotropy provided for the thin-film magnetic cores 2, 3, however, isnot perfectly arranged in the direction of easy axis over the wholemagnetic film, and usually remains dispersed. Since the dispersion ofanisotropy causes fluctuation in output and the Barkhausen noise, acurrent is caused to flow in the direction of hard axis of the magnetichead of present invention, as indicated by arrow X in FIGS. 4 and 5.

As the current flows in the direction of hard axis, magnetic fields H₁,H₂ are generated in the direction of easy axis Y in the upper thin-filmmagnetic core 3. As a result, the magnetic fields H₁, H₂ adjust thedirection of magnetization of the thin-film magnetic core 3 into thedirection of easy axis, thus stabilizing the magnetic domain.Particularly, when the pair of upper and lower magnetic films 6, 7 arestacked as in the upper thin-film magnetic core 3, the upper and lowermagnetic films 6, 7 are desirably coupled with each other to form thestructure of single magnetic domain, thus producing a highly stablestate without having magnetic domain walls.

Consequently, in the thin-film magnetic head of the above structure, ifthe current in the direction of hard axis is caused to flow through atleast one of the thin-film magnetic cores 2, 3 after recording, theturbulent magnetic domain due to the recording magnetic field can beadjusted and the fluctuation in output and generation of the Barkhausennoise can be restricted. Thus, it is possible to implement satisfactoryrecording/ reproduction.

Embodiment 2

In Embodiment 2, the present invention is applied to an MR head forreproduction.

In an MR head 12 shown in FIG. 6, an MR element 13 as a magnetic sensorcomposed of a single-layer or multi-layer magnetic thin film havingmagnetoresistance effect is located in a space forming a predeterminedreproduction gap G_(R) provided between a pair of shield cores, that is,an upper shield core 14 and a lower shield core 15. In the space betweenthese shield cores 14, 15, a bias conductor 16 is arranged traversingthe MR element 13.

One of the shield cores, for example, the shield core 14, has its oneend, on the side of the reproduction gap G_(R), electrically connectedto the MR element with a non-magnetic conductor 17a provided betweenthem. The non-magnetic conductor 17a serves both as an electrode and asa gap film. The MR element 13 has its other end electrically connectedto an electrode 17b, so as to be taken out to outside. The shield core14 electrically connected to the MR element 13 has a structure in whichtwo layers of soft magnetic thin films 14a, 14b separated with anon-magnetic thin film 14c between them are stacked. The shield core 14has its other end electrically connected to an electrode 17c, so as tobe taken out to outside.

In the MR head as described above, a sense current i directed from theelectrode 17b on the rear side to the non-magnetic conductor 17a iscaused to flow through the MR element 13, as shown in FIG. 7. The sensecurrent i flows through the MR element 13 and then through thenon-magnetic conductor 17a on the front side thereof to the upper shieldcore 14. The current flowing through the shield core 14 is in thedirection of hard axis.

As the sense current i flows through the upper shield core 14, magneticfields H₃, H₄ in the direction of easy axis, as indicated by an arrow inFIG. 8, are generated in the shield core 14. The magnetic fields H₃, H₄adjust the direction of magnetization of the shield core 14 into thedirection of easy axis, thus stabilizing the magnetic domain.Particularly, since the two layers of magnetic films 14a, 14b arestacked in the upper shield core 14, the upper and lower magnetic films14a, 14b are desirably coupled with each other to form the structure ofsingle magnetic domain, thus producing a highly stable state withouthaving magnetic domain walls.

In this manner, in the MR head of the present embodiment, since thesense current i constantly flows through the shield core 14, themagnetic domain of the shield core is constantly stable, withfluctuation in output and generation of the Barkhausen noise beingrestricted. Thus, it is possible to implement satisfactoryrecording/reproduction.

Embodiment 3

In Embodiment 3, the present invention is applied to an MR inductivehead of a magnetic disk device, such as, a hard disk.

The MR inductive head is composed of the MR head 12 of Embodiment 2 andan inductive head stacked thereon, as shown in FIG. 9. That is, theupper magnetic film 14a of the shield core 14 of stacked structure isused as a recording core, and a magnetic core 18 is provided on theupper magnetic film 14a with the predetermined recording gap G_(W)between them. A head winding 19 as a spiral conductive coil is providedaround the magnetically connecting portion of the magnetic core 18 withthe upper magnetic film 14a.

The MR inductive head is provided with the shield core 15 of the MR headon a base or substrate 20 of Al₂ O₃ -TiC, a protection film layer 21stacked on the magnetic core 18, and a non-magnetic insulation materialcharged or stacked in the gap. The front end surface of the MR inductivehead in which the reproduction gap G_(R) and the recording gap G_(W) areprovided is a so-called air bearing surface (ABS) 22 as the surfacefacing a magnetic recording medium, such as, a hard disk. The shieldcore 14 in the intermediate position is grounded, for achieving areduction of noise and prevention of electrostatic destruction.

Meanwhile, the reproduction track width T_(R) of the reproduction gapG_(R) and the recording track width T_(W) of the recording gap G_(W) arein the relation shown in FIG. 10.

In the MR inductive head as described above, as recording has beencarried out with the inductive head, residual magnetization remains inthe shield core 14, causing the magnetic domain to be turbulent.However, since the sense current i flows in the direction of hard axisthrough the shield core 14, the magnetic fields H₃, H₄ generated by thesense current i stabilizes the magnetic domain after recording.Accordingly, even if the operation is switched from recording toreproduction, the stable magnetic domain prevents fluctuation in outputand generation of the Barkhausen noise.

Then, an example of the circuit connected to the MR heads of Embodiments2 and 3 and to the MR inductive head is shown in FIG. 11.

In FIG. 11, an MR head 23 substantially corresponds to the MR element13. However, while the MR element 13 is electrically connected to theshield core 14, the MR head 23 has its one end grounded and its otherend provided with a DC as the sense current, as later described, and hasthe output of the other end supplied through a DC cutting capacitor 24to the base of a common emitter transistor 25 as an initial amplifier.

The connecting point of the base of the transistor 25 and the capacitor24 is connected with a current source 26 for supplying the base current,while the transistor 25 has its collector connected with a load resistor27. If the value of resistance of the MR head through which the sensecurrent flows is changed by the signal magnetic field, the change istaken out as a change in voltage. The change in voltage is then suppliedthrough the DC cutting capacitor 24 to the common emitter transistor 25,where it is amplified so as to be outputted.

The MR head 23 is supplied with a DC sense current and a decrement ACdemagnetization current. That is, an output voltage from a sense currentcontrol voltage generation circuit 28 and an output voltage from ademagnetization current control voltage generation circuit 29 are addedtogether by an adder 30 and the resulting voltage is transmitted to ag_(m) amplifier 31 as a voltage-current converter, where it is convertedinto a current to be transmitted to the MR head 23.

A concrete example of the sense current and the demagnetization currentin this case is shown in FIG. 12. In FIG. 12, as thereproduction/recording (R/W) mode changes as shown in FIG. 12A, thesense current of DC having a current value of Is is provided in thereproduction (R) mode, as shown in FIG. 12B. A decrement DC having aninitial current amplitude value of ±I_(d), as shown in FIG. 12C, issuperposed on the sense current, thus producing a current as shown inFIG. 12D.

In the example of FIG. 12, the sense current and the demagnetizationcurrent are caused to flow simultaneously at timing t₁ for switching theoperation from the recording (W) mode to the reproduction (R) mode.However, it is also allowable to cause only the demagnetization currentto flow on completion of recording, that is, at timing t₁, and to causethe sense current to flow at timing t₃ when the flow of thedemagnetization current is completed, as shown in FIG. 11.

Such timing control can be realized using the structure as shown in FIG.13.

In FIG. 13, the sense current control voltage generation circuit 28 andthe demagnetization current control voltage generation circuit 29 areprovided with on/off control signals from a timing control circuit 32.The timing control circuit 32 is provided with a reproduction/recordingswitching control signal R/W. At timing t₁ when the switching controlsignal R/W is changed from recording (W) to reproduction (R), thedemagnetization current control voltage generation circuit 29 is turnedon to generate a decrement AC voltage. The sense current control voltagegeneration circuit 28 is turned on at timing t₁ (in the case of FIG. 12)or at timing t₃ (in the case of FIG. 14) after the amplitude of thedemagnetization current reaches 0, thus generating a DC demagnetizationcurrent control voltage.

The demagnetization current control voltage generation circuit 29includes a pyramidal wave generation circuit 29a, an AC signalgeneration circuit 29b, and a multiplier 29c for multiplying outputsignals from the circuits 29a, 29b. The pyramidal wave generationcircuit 29a is supplied with amplitude data DA for setting the initialcurrent amplitude value ±I_(d) of the demagnetization current anddecrement time data DT for setting the decrement time of the amplitude,while the AC signal generation circuit 29b is supplied with frequencydata DF for setting frequency of the AC.

A pyramidal wave voltage of the amplitude and the decrement time basedupon the data DA and DT is outputted from the pyramidal wave generationcircuit 29a, and an AC of the frequency based upon the data DF isoutputted from the AC signal generation circuit 29b. These outputsignals are multiplied by the multiplier 29c and is outputted as thedecrement AC voltage signal as shown in FIG. 12C.

The initial amplitude value ±I_(d) of the demagnetization current is setas a value sufficiently large for the MR head of FIG. 6 or the MRinductive head of FIG. 9 to perfectly exhibit the structure of singlemagnetic domain, and this initial amplitude value ±I_(d) is changed to adecrement repeat wave, thus converging the magnetic domain of the shieldcore in a constant stable state. In the case of FIG. 12, if the sensecurrent and the demagnetization current are simply added together, thepeak value exceeds I_(d) or decreases below -I_(d). However, since thecurrent exceeding I_(d) is unnecessary, the current may be limited atI_(d), as shown in FIG. 12D. If I_(d) is of a value not so largecompared with the sense current I_(s), there is a possibility that thereciprocal balance of the demagnetization current is disturbed, causingineffective magnetization. In this case, it is effective to stop theflow of the sense current during the flow of the demagnetization currentand to allow the sense current to flow when the demagnetization currentreaches 0.

Thus, by superposing the demagnetization current of decrement repeatwave decreasing from the current level large enough for the shield core14 to perfectly exhibit the structure of single magnetic domain at thestart of reproduction, onto the sense current for flowing, the turbulentmagnetic domain of the shield core 14 on recording can be adjusted to aconstant stable state on reproduction. Therefore, the bias magneticfield applied to the MR element 13 and the magnetic path to the signalmagnetic field are stabilized, thus stabilizing the reproduction signal,having no Barkhausen noise. Consequently, in the present embodiment, thetrack recording density which was conventionally restricted byinstability of the reproduction signal can now be increased. Also, sincethe shield core width which was conventionally able to be reduced onlyto a certain extent because of instability of the magnetic domain can befurther reduced now, crosstalk from adjacent tracks taken up through theshield core can be reduced. Thus, the track density can be improved,increasing the storage capacity of the magnetic disk device.

Several examples of the structure of a reproduction circuit employed forthe embodiments of the present invention will now be described indetail, with reference to the drawings.

An example of the circuit in which a common emitter transistor is usedas an initial amplifier of the MR head is shown in FIG. 15. As shown inFIG. 15, the MR head 23 is supplied with a sense current from a sensecurrent generation circuit (current source) 33, and has its terminalvoltage transmitted through the capacitor 24 to the base of the commonemitter transistor 25. The connecting point of the base of thetransistor 25 and the capacitor 24 is connected with the current source26 for supplying a base current. The transistor 25 has its collectorconnected with the load resistor 27.

In addition, an output signal from the demagnetization current controlvoltage generation circuit 34 is provided through a g_(m) amplifier 35as a voltage-current converter to the connecting point of the sensecurrent generation circuit 33 and the MR head 23. The demagnetizationcurrent control voltage generation circuit 34, similar to thedemagnetization current control voltage generation circuit 29 of FIG.11, generates a decrement AC voltage, which is converted by the g_(m)amplifier 35 into a current to be supplied to the MR head 23 as thedecrement repeat wave current decreasing from the level large enough forthe shield core to perfectly exhibit the structure of single magneticdomain at the start of reproduction.

Thus, two current sources are employed, that is, the sense currentgeneration circuit 33 supplying the sense current and thedemagnetization current control voltage generation circuit 34 supplyingthe voltage output signal to be converted by the g_(m) amplifier 35 intothe current as the demagnetization current to be supplied. In theembodiment shown in FIG. 15, the timing setting for the demagnetizationcurrent and the sense current as explained with reference to FIGS. 12and 14 can be implemented, with a method of starting the flow of thedemagnetization current and the sense current simultaneously at thestart of reproduction, as shown in FIG. 12 or with a method of startingthe flow of the sense current on completion of the flow of thedemagnetization current, as shown in FIG. 14.

That is, in the case where the demagnetization current and the sensecurrent start to flow simultaneously immediately after completion ofrecording at timing t₁, as shown in FIG. 12, the reduction in switchingtime for switching of the reproduction mode to the actually reproduciblestate is advantageous. In this case, however, it may be better to causethe sense current to flow after completion of the flow of thedemagnetization current having the initial amplitude value of ±I_(d), asshown in FIG. 14, depending upon conditions demanded of thedemagnetization current in terms of magnetization effects.

FIG. 16 shows an example in which a common base transistor 37 isemployed as an initial amplifier for taking out signals from the MR head36. In FIG. 16, the transistor 37 has its emitter grounded via theabove-described MR head. Also, the transistor 37 has its base suppliedwith a sense current control voltage signal from a sense current controlvoltage generation circuit 38, and has its collector connected with aV_(cc) source through a load resistor 39.

In addition, a decrement AC voltage output signal from a demagnetizationcurrent control voltage generation circuit 40 is converted by a g_(m)amplifier 41 as a voltage-current converter into a current signal to besupplied between the transistor 37 and the MR head 36. A voltage source,for example, can be used for the sense current control voltagegeneration circuit 38. The sense current is determined by the voltage ofthe voltage source, an emitter voltage determined by the transistor 37,and the resistance value of the MR head 36.

The example shown in FIG. 16 can be considered to include two currentsources, that is, the current source obtained by directly applying theoutput voltage from the sense current control voltage generation circuit38 to the base of the transistor 37, and the current source obtained bythe g_(m) amplifier 41. It is a matter of course that, in the embodimentof FIG. 16, the method of starting the flow of the demagnetizationcurrent and the sense current simultaneously at the start ofreproduction, as shown in FIG. 12 and the method of starting the flow ofthe sense current on completion of the flow of the demagnetizationcurrent, as shown in FIG. 14, can be employed.

In this case, the initial current amplitude value ±I_(d) of thedemagnetization current is set at a value large enough for the shieldcore of an MR head, as later described, to perfectly exhibit thestructure of single magnetic domain. Thus, by causing thedemagnetization current of decrement repeat wave decreasing from theinitial amplitude value ±I_(d) to flow through the shield core, it ispossible to perfectly adjust the magnetic domain which has becometurbulent on recording.

Embodiment 4

In Embodiment 4, the present invention is applied to an MR inductivehead in which recording/reproduction is carried out with a pair ofmagnetic films.

The MR inductive head of the present embodiment has a pair of first andsecond thin-film magnetic cores 43, 44 stacked on a substrate 42, whichare used both as recording magnetic cores in recording and asreproduction magnetic cores in reproduction, as shown in FIG. 17.

The first thin-film magnetic core 43 has its one end exposed to an ABSsurface 47 as the surface facing the magnetic recording medium, andextends backward in a direction perpendicular to the ABS surface 47.

On the other hand, the second thin-film magnetic core 44 has a stackedstructure in which two soft magnetic thin-films 44a, 44b are stackedwith a non-magnetic thin film 44c between them. Similar to the firstthin-film magnetic core 43, the second thin-film magnetic core 44 hasits one end exposed to the ABS surface 47 and extends backward in thedirection perpendicular to the ABS surface 47.

Also, the second thin-film magnetic core 44 has its distance from thefirst thin-film magnetic core 43 narrowed at the front end on the sideof the ABS surface 47, and has its distance from the first thin-filmmagnetic core 43 widened at the central portion provided with a headwinding 45. The second thin-film magnetic core 44 is then magneticallyconnected to the first thin-film magnetic core 43 on the rear side.

Between the first and second thin-film magnetic cores 43, 44, the spiralhead winding 45 is buried in an insulation layer 46 in such a manner asto surround the magnetically connecting portion of the thin-filmmagnetic cores 43, 44.

Also, between the first and second thin-film magnetic cores 43, 44, anMR element 48 is provided at a portion close to the ABS surface 47 asthe surface facing the magnetic recording medium. The MR element 48 hasits longitudinal direction perpendicular to the ABS surface 47, and hasone end exposed to the ABS surface 47.

At the front end of the MR element 48, a non-magnetic conductor 49a isstacked, serving both as an electrode and as a gap film. Thenon-magnetic conductor 49a is electrically connected to the secondthin-film magnetic core 44. The rear end of the MR element 48 iselectrically connected with an electrode 49b for causing a sense currentto flow through the MR element 48 so as to be taken out.

Between the non-magnetic conductor 49a and the electrode 49b, a biasconductor 50 for providing a bias magnetic field in a predetermineddirection to the MR element 48 is provided. The bias conductor 50 isprovided in the direction substantially orthogonal to the longitudinaldirection of the MR element 48, that is, in the vertical direction inFIG. 17, traversing the MR element 48. Both ends of the bias conductor50 carry a bias current from a DC power source. Consequently, the DCsprovided from both terminals flow in the direction of track width, and aresulting bias magnetic field is applied in the longitudinal directionof the MR element 48.

In the MR inductive head as described above, the inductive head isconstituted by the first and second thin-film magnetic cores 43, 44 andthe head winding 45, while the shield MR head is constituted by the MRelement 48 provided with the non-magnetic conductor 49a and theelectrode 49b on the front and rear sides thereof, respectively, and thefirst and second thin-film magnetic cores 43, 44 sandwiching the biasconductor 50 from above and below.

A protection film layer 51 for protecting the MR inductive head isformed on the second thin-film magnetic core 44. The reproduction trackwidth T_(R) and the recording track width T_(w) in the MR inductive headare in the relation as shown in FIG. 18.

In this MR inductive head, since recording and reproduction are carriedout with the second thin-film magnetic core 44 as a common magneticbody, residual magnetization remains after recording, causing themagnetic domain to be turbulent. However, since the sense current flowsthrough the second thin-film magnetic core 44 in the direction of hardaxis via the MR element 48, the magnetic field generated by the sensecurrent stabilizes the magnetic domain. Thus, even when the mode isswitched from recording to reproduction, the stable magnetic domainserves to prevent fluctuation in output and generation of the Barkhausennoise.

It is to be understood that the present invention is not limited to theabove-described embodiments. For example, though the bias magnetic fieldgenerated by the bias current flowing through the bias conductor is usedas the bias to be applied to the MR element, the bias magnetic field maybe applied with a polarized hard magnetic body thin-film providedinstead of the bias conductor. The present invention can also apply toan MR head which does not require a bias conductor, such as, a so-calledshunt bias conductor. In addition, though the shield MR head isexplained in the embodiment, the present invention can also apply to ayoke MR head, replacing the shield core in the embodiment.

As is clear from the above description, in the thin-film magnetic headof the present invention, one of the thin-film magnetic cores is formedof two layers of magnetic films stacked with a non-magnetic film betweenthem, and the current flows through the thin-film magnetic core in thedirection of hard axis thereof. Thus, the turbulent magnetic domainafter recording can be adjusted by the magnetic field generated by thecurrent flowing through the thin-film magnetic core, producing thestable magnetic domain.

Also, in the MR head of the present invention, the MR element iselectrically connected with one of a pair of shield cores having the MRelement between them, and the shield core is formed of two magneticfilms and a non-magnetic film held between them. Thus, the sense currentflowing through the MR element can also flow through the shield core inthe direction of hard axis thereof, demagnetizing the shield core.

Accordingly, even if the magnetic domain of the shield core becomesturbulent on recording, it can be adjusted into a constant stable stateon reproduction. Therefore, since the bias magnetic field applied to theMR element and the magnetic path to the signal magnetic field arestabilized, generation of the Barkhausen noise can be prevented andreproduction signals can be stabilized, thus improving the trackrecording density which was conventionally limited by instability of thereproduction signals. Also, since the width of the shield core which wasconventionally able to be reduced only to a certain extent because ofinstability of the magnetic domain can be further reduced, crosstalkfrom adjacent tracks taken up through the shield core can be reduced,and track density can be increased. Thus, the storage capacity of themagnetic disk device can be enlarged.

In addition, in the MR inductive head of the present invention, acurrent flows through the second thin-film magnetic core as the commonmagnetic body of the MR head and the inductive head in the direction ofhard axis of the second thin-film magnetic core. Therefore, theturbulent magnetic domain after recording can be adjusted by themagnetic field generated by the current flowing through the thin-filmmagnetic core, producing a stable magnetic domain. Accordingly, theturbulent structure of magnetic domain of the shield core afterrecording with the inductive head can be stabilized by the magneticfield generated by the current flowing through the second thin-filmmagnetic core, thus significantly reducing fluctuation in output andgeneration of the Barkhausen noise.

What is claimed is:
 1. An MR inductive head system comprising aninductive head and magnetoresistive head formed on one substrate,wherein:the inductive head has two shield cores with a gap formedbetween the shield cores at a forward end thereof; the magnetoresistivehead is provided within the gap of the inductive head; and one of theshield cores is used as a shield for the magnetoresistive head and iscomprised of two soft magnetic layers and a non-conductive layer betweenthe two soft magnetic layers, said MR inductive head system furthercomprising:a sense signal source for generating a dense signal; ademagnetizing signal source for generating a demagnetizing signal; anadder which adds together the sense and demagnetizing signals togenerate a current from said added signals; and a conductive membercoupling the current to said one shield, the current being effective tostabilize the magnetic domain of the magnetoresistive head shield. 2.The MR inductive head system as claimed in claim 1, wherein theinductive head has a current caused to flow through the magnetoresistivehead shield in a direction of hard axis thereof.
 3. The MR inductivehead system of any of claims 2 and 1, wherein, said current comprises analternating current demagnetizing signal with a decrementing amplitude.4. The MR inductive head system of any of claims 2 and 1, comprising acircuit including:a sense current generator as said sense signal source,said sense current generator generating a sense current and beingcoupled to said magnetoresistive head; a demagnetizing current generatoras said demagnetizing signal source, said demagnetizing currentgenerator generating a demagnetizing current and being commonly coupledto said magnetoresistive head with said sense current generator; acommon emitter transistor; a capacitance element coupling said sense anddemagnetizing currents to the base of said transistor.
 5. The MRinductive head system of any of claims 2 and 1 comprising a circuitincluding:a common base transistor; a demagnetizing current generator assaid demagnetizing signal source, said demagnetizing current generatorgenerating a demagnetizing current which is coupled to the collector ofsaid common base transistor; and a sense current control voltagegenerator as said sense signal source, said sense current controlvoltage generator generating a sense current voltage which is coupled tothe base of said common base transistor.
 6. The MR inductive head systemof any of claims 2 and 1 comprising a circuit including:ademagnetization current control voltage generator as said demagnetizingsignal source, said demagnetization current control voltage generatorgenerating a demagnetization current voltage; a sense current controlvoltage generator as said sense signal source, said sense currentcontrol voltage generator generating a sense current voltage; a summeroperatively coupled to sum said demagnetization current voltage and saidsense current voltage; a voltage-to-current converter coupled betweensaid magnetoresistive head and said summer; and a common emittertransistor whose base is commonly coupled to the magnetoresistive headand an output of said voltage-to-current converter.